BCGA CODE OF PRACTICE CP 22

Transcription

1 BCGA CODE OF PRACTICE CP 22 BULK LIQUID ARGON OR NITROGEN STORAGE AT PRODUCTION SITES Revision 1 : 2002

2 BCGA CODE OF PRACTICE CP 22 BULK LIQUID ARGON OR NITROGEN STORAGE AT PRODUCTION SITES Revision 1 : 2002 Copyright 2002 by British Compressed Gases Association. First printed All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, without permission from the publisher: BRITISH COMPRESSED GASES ASSOCIATION 4a Mallard Way, Pride Park, Derby, DE24 8GX Tel Website : ISSN BCGA CP22 Rev

3 PREFACE The various publications issued by the British Compressed Gases Association have the objective of establishing consistency in design, construction practices and user operational and maintenance procedures, in order to establish high standards of reliability and safety in the interests of employers, employees and the general public. The Association endeavours to compile these documents using the best sources of information known at the date of issue. The information is used in good faith and belief in its accuracy. The publications are intended for use by technically competent persons and their application does not, therefore, remove the need for technical and managerial judgement in practical situations and with due regard to local circumstances, nor do they confer any immunity or exemption from relevant legal requirements, including by-laws. The onus of responsibility for their application lies with the user. The Association, its officers, its members and individual members of any Working Parties can accept no legal liability or responsibility whatsoever, howsoever arising, for the consequences of the use or misuse of the publications. For the assistance of users, references are given, either in the text or Appendices, to publications such as British, European and International Standards and Codes of Practice, and current legislation that may be applicable. The intention of BCGA is that this document should be read and used in the context of these references where the subjects have a bearing on the local application of the processes or operations carried out by the user. BCGA s publications are reviewed, and revised if necessary, at threeyearly intervals. Readers are advised to check the list of publications on the Association s website to ensure that the copy in their possession is the current version. BCGA CP22 Rev

4 C O N T E N T S Section Page Terminology and Definitions 1 Introduction 2 Scope 2 1. GENERAL DESIGN CONSIDERATIONS Properties of Argon and Nitrogen Precautions Asphyxiation Cleaning for Argon or Nitrogen Service Embrittlement of Materials Cryogenic Burns Hot Work Insulation Materials Regulations and Codes Design of Installation Design and Manufacture of the Tank Tank Inspection (during manufacture) Pressure Relief Devices Under-pressure Prevention Devices Pits Electrical Equipment Couplings Lighting Pipework Control and Instrumentation Outer Jacket Purge 9 2. LAYOUT OF THE INSTALLATION General Safety Distances Basis Definitions and Intentions On-Site Risks Off-Site Risks 11 BCGA CP22 Rev

5 Section Page 2.3 Location of Installation Outdoor Installation Protection against Electrical Hazards Level and Scope Position of Vents Vapour Clouds Diversion of Spillage Protection of Other Areas Liquid Transfer Area Location of Area Construction of Access Apron Control of Tanker Operation Liquid Transfer Pumps Isolation Valves Emergency Isolation Valves Secondary Isolation Valves Process Isolation Valves Foundations ACCESS TO THE INSTALLATION Personnel Access to Installation Controls Notices General Precautions Identification of Contents Legibility of Notices Operating and Emergency Instructions TESTING AND COMMISSIONING Testing of Installation Pressure Test Pressure Relief Devices Under-pressure Prevention Devices Supports 17 BCGA CP22 Rev

6 Section Page 4.2 Adjustment of Process Control Devices Posting of Notices Commissioning OPERATION, INSPECTION AND MAINTENANCE Operation of the Installation Periodic Inspection and Maintenance General Tank Installation Inner Vessel Pressure Relief Devices Emergency Isolation Valve(s) Ancillary Equipment Opportunity Examinations TRAINING AND PROTECTION OF PERSONNEL Training of Personnel Permit to Work Entry into Vessels Emergency Procedures REFERENCES 23 Appendix 1 Typical Bulk Storage Tank Systems 26 Appendix 2 Burns due to Very Cold Liquefied Gases 30 Appendix 3 Safety Distances 32 Appendix 4 Appendix 5 Plan View of Liquid Transfer Area, Access Apron and Tanker Standing Area 33 Relief Device Inspection, Testing and Examination 34 History and Objectives of BCGA 38 BCGA CP22 Rev

7 TERMINOLOGY & DEFINITIONS 1. Shall: Indicates a mandatory requirement for compliance with this Code of Practice. 2. Should: Indicates a preferred requirement but is not mandatory for compliance with this Code of Practice. 3. May: Indicates an option available to the user of this Code of Practice. 4. Tank: Indicates an assembly, complete with a piping system, of an inner vessel and an outer jacket to contain insulation. The insulation space may be at atmospheric pressure, slightly above atmospheric pressure or subject to a vacuum. See Appendix Vessel: Indicates a pressure vessel, which may or may not be insulated. 6. Outer Jacket: Indicates a shell surrounding an inner vessel, containing an insulating system, e.g. vacuum, granular or fibrous insulant. 7. Access Apron: Indicates an area between the tank and a tanker where the process operating controls on both tank and tanker are accessible to the operator during filling/discharging. This area will normally have provision for diverting any liquid spillage. 8. Liquid Transfer Area: Indicates an area adjacent to the tank, which surrounds the tanker, when the latter is in the filling/discharging position, and which includes the access apron. 9. Competent Person: The Competent Person should have such practical and theoretical knowledge and actual experience of the type of plant which he has to examine as will enable him to detect defects or weaknesses, which it is the purpose of the examination to discover, and to assess their importance in relation to the strength and function of the plant. Equivalent levels of knowledge and experience are also required for Competent Persons engaged in the writing or certifying of Written Schemes of Examination. 10. Examination: Means examination in accordance with the Written Scheme of Examination (as detailed in the Pressure Systems Safety Regulations 2000 (22)). 11. Production Site: Is typically where liquid nitrogen or argon is produced from an air separation unit and stored on site. 12. Numerals in brackets refer to References (Section 7). 1

8 INTRODUCTION In 1985 the Industrial Gases Committee (IGC) of the Commission Permanente Internationale (CPI) published a document, IGC 25/85/E (1) entitled Bulk Liquid Argon and Nitrogen Storage at Production Sites. The British Compressed Gases Association has recognised the need to produce an equivalent document specifically for the United Kingdom. This BCGA document is intended as a Code of Practice for the guidance of UK companies directly associated with the design, operation and maintenance of bulk liquid storage installations. The objective of the BCGA document is to make reference to UK legislation and British Standards, where these apply to liquid argon and nitrogen systems, and to take into account the specific practices of the UK industrial gas companies, particularly in relation to safety distances. It is recognised that sites operated by industrial gas producers have a level of expertise and specialist knowledge that is not available to general industrial and other users. This Code of Practice is based generally on the BCGA Document CP20 (2) and the IGC Document 25/85/E. The BCGA wishes to acknowledge the work carried out by the committees that prepared documents CP20 and 25/85/E. The increase in recent years in the size of production capacity of air separation plants has led to a corresponding increase in the capacity of liquid storage installations at production sites. It has therefore become more important to consider at the design stage the potential hazards associated with liquid, the consequence and effects on the local environment of a major release of liquid, and the preventive measures required. All new storage installations on production sites shall comply with this BCGA Code of Practice. Major modifications to existing production site liquid argon and liquid nitrogen storage should also comply with this Code of Practice, but it is not intended to apply retrospectively to existing production site storage installations. SCOPE A bulk liquid argon or nitrogen storage installation on a production site is defined for the purposes of this Code of Practice as the total fixed assembly of liquid storage tank(s) and other equipment such as pumps, controls and ancillary equipment required to discharge from the storage into pipelines or to transfer liquid to or from road vehicles. The installation also includes the liquid transfer area for road vehicles. The facilities for filling rail vehicles are not specifically covered in this Code of Practice, although the provisions of this Code of Practice will generally still apply to the liquid storage part of the rail fill installation. This Code of Practice covers liquid argon and liquid nitrogen storage installations on production sites where the storage installation is connected to the production process plant. Individual vessel capacity for such storage is normally greater than 250,000 litres of liquid. 2

9 However, where the individual vessel capacity is less than 250,000 litres but the storage installation is connected to the production process the installation shall also comply with this Code of Practice. Where a liquid argon or nitrogen storage installation on a production site has a net individual vessel capacity of less than 250,000 litres and the storage is not connected to the production process, the BCGA Code of Practice CP21 - Bulk Liquid Argon and Nitrogen Storage at Users Premises (3), may be applied as an alternative. The process systems of the production plant (such as compressors, heat exchangers, distillation columns and turbo expanders) are specifically excluded from the scope of this Code of Practice, as are gaseous distribution pipelines and related equipment. The liquid feed pipeline from the plant into the storage tank shall be considered as part of the production plant. For the purposes of this Code of Practice, cluster tanks (i.e., multiple inner vessels in a single outer jacket) are considered as a single tank whose capacity is the sum of the capacities of the individual inner vessels. Where the storage contains multiple products including oxygen, the BCGA Code of Practice CP20 (2) for oxygen storage shall apply to the whole installation, based on the sum of all the oxygen vessel capacities. See Appendix 1. Pumping systems often form part of the liquid storage installation. It is recognised that the design and installation of these pump systems is a complex subject. No detailed recommendations are given in this Code of Practice but due consideration should be given to: The accepted principles of good practice for cryogenic service The prevention of mal-operation of the pump(s) Siting the pump(s) to provide personnel protection in the event of a spill Adequate access, inspection and maintenance procedures. For cylinder filling depots operated by industrial gas suppliers, where the liquid storage vessel capacity is normally less than 250,000 litres, this Code of Practice is only applicable where the vessel is connected to the production process. However, the provisions in the BCGA Code of Practice CP21 Liquid Argon and Nitrogen storage at Users Premises (3) in relation to safety distances, periodic inspection and testing and the liquid transfer area may be applied as an alternative. 3

10 1. GENERAL DESIGN CONSIDERATIONS 1.1 Properties of Argon and Nitrogen Gaseous argon and gaseous nitrogen are colourless, odourless and tasteless. They are non-toxic but do not support life or combustion. Their physical properties are: Argon Nitrogen Content in air Vol% Gas density at bar, 15 C kg/m³ Boiling temperature at bar C Liquid density at bar and boiling point kg/l At ambient conditions 1 litre of liquid argon produces approximately 830 litres of gas and 1 litre of liquid nitrogen produces approximately 690 litres of gas. The cold vapours are substantially heavier than air and may accumulate in pits and trenches. 1.2 Precautions Asphyxiation Argon and nitrogen may produce local oxygen-deficient atmospheres, which will result in asphyxia if breathed. This is especially true in confined spaces. Atmospheres containing less than 18% oxygen are potentially dangerous and entry into atmospheres containing less than 19.5% is not recommended. Exposure to atmospheres containing less than 10% oxygen can result in brain damage or death. Asphyxia due to oxygen deficiency is often rapid with no prior warning to the victim. A general indication of what is liable to happen in oxygen-deficient atmospheres is given in the following table, but it should be appreciated that the reactions of some individuals can be very different from those shown. O 2 Content Vol% Effects and Symptoms (at atmospheric pressure) Diminution of physical and intellectual performance without the person s knowledge Possibility of fainting after a short period without prior warning. 6-8 Fainting within a few minutes, resuscitation possible if carried out immediately. 0-6 Fainting almost immediate, death ensues. Brain damage even if rescued. 4

11 Attempts to rescue affected persons from confined spaces or where oxygendeficient atmospheres may be present should be made only by persons who are wearing and trained in the use of breathing apparatus and who are familiar with confined space entry procedures. The requirements of the Confined Spaces Regulations (4) shall be met. The victim may well not be aware of the asphyxia. If any of the following symptoms appear in situations where asphyxia is possible and breathing apparatus is not in use, move the affected person immediately to the open air, following up with artificial respiration if necessary. i. Rapid and gasping breath ii. Rapid fatigue iii. Nausea iv. Vomiting v. Collapse or incapacity to move vi. Unusual behaviour Cleaning for Argon or Nitrogen Service Although neither argon nor nitrogen reacts with oil or grease, it is good practice to apply a high standard of cleanliness, similar to that required for oxygen installations (5) & (6). BS EN provides a general standard for cleanliness for vessels in cryogenic service (27) Embrittlement of Materials Many materials such as carbon steels and plastics are brittle at low temperatures and the use of appropriate materials, for the service conditions prevailing, is essential. Metals suitable for liquid argon or nitrogen service are 9% nickel steel, 18/8 stainless steel and other austenitic stainless steels, copper and its alloys and aluminium alloys. PTFE (polytetrafluoroethylene) is the most widely used plastic material for sealing purposes in liquid argon or nitrogen service but other reinforced plastics are also used. For further information on materials see BS 5429 (7) Cryogenic Burns Severe damage to the skin may be caused by contact with liquid argon or nitrogen, cold gaseous argon or nitrogen, or with non-insulated pipes or receptacles containing liquid argon or nitrogen. For this reason, gloves and eye protection shall be worn when handling equipment in liquid or gaseous argon or nitrogen service. All the safety aspects of handling cryogenic liquid argon or nitrogen cannot be covered adequately in this Code of Practice. The reader is therefore referred to the 5

12 British Cryoengineering Society s publication Cryogenics Safety Manual (8) for further information. (See Appendix 2) Hot Work Hot work shall not be performed in the vicinity of the installation without a Permit to Work. (See 6.2) Insulation Materials Ambient air will condense on un-insulated pipes and vessels containing liquid nitrogen, so causing local oxygen enrichment of the atmosphere. Insulating materials should be chosen bearing in mind that oxygen enrichment may occur. 1.3 Regulations and Codes This Code of Practice describes minimum requirements. All relevant statutory regulations shall be applied and relevant codes of practice, standards and specifications shall be taken into account in the designs and installations covered by this Code of Practice. (See References, Section 7). 1.4 Design of Installation Design and Manufacture of the Tank Tanks shall be designed, manufactured and installed in accordance with recognised pressure vessel, storage tank and piping codes, e.g. PD 5500 (9)/BS 7777 Part 4 (10) or ANSI/ASME B31.3 (11), and shall comply with the production site operator s specifications. Consideration shall be given to the requirements of the Pressure Equipment Regulations (28) where appropriate. Tanks shall be designed to withstand wind-loads in accordance with the appropriate design codes and with BS (12) Tank Inspection (During Manufacture) Pressure vessels and storage tanks shall be inspected and approved during manufacture by a Competent Person. Butt welds in the inner vessel shall be radiographed in accordance with the design code. If required, prior to its first use, the Competent Person shall certify the vessel as suitable for the duty within defined operating limits for a defined period. Any modification to the system shall be carried out in accordance with the applicable design code; some modifications may require consultation with the vessel supplier. 6

13 1.4.3 Pressure Relief Devices Pressure relief devices shall be provided to prevent overpressure of the inner vessel. The devices shall be suitable for the prevailing environmental conditions. For the protection of the inner vessel a minimum of two independent pressure relief devices shall be provided. The capacity of each device shall be such that should one malfunction or be removed for maintenance the vessel shall be adequately protected. Both pressure relief devices will normally be in service. Consideration shall be given to the design of the system to allow isolation of individual pressure relief devices to facilitate their periodic testing or replacement. Methods of isolation are commonly a three-way valve or isolation valve upstream of each relief device. The system installed shall ensure that the tank is fully protected at all times. Three-way valves shall be provided with a position indicator showing which relief devices are on line. The design relieving capacity of the inner vessel pressure relief system shall be based upon the worst foreseeable combination of the operational and upset conditions, e.g.: Boil-off rate including loss of vacuum where applicable Flash gas from plant-make, from road or rail tankers and pumps recycling product Malfunction of control valves in pressure raising systems or the production process. Barometric pressure changes The pipes and valves connecting the vessel to pressure relief devices and the vent piping shall be adequately sized for the flow conditions in accordance with a relevant code. Excess pressure drop in the upstream system can lead to relief valve chattering causing reduction in capacity and valve damage. Vent pipes shall be correctly supported and designed to prevent blockage by ice and other foreign matter. Thermal relief devices shall be provided to prevent overpressure in systems where liquid or cold gas can be trapped. Relief valves shall be in accordance with a recognised standard e.g. BS 6759 (13). Where bursting discs are installed they shall be in accordance with a recognised standard e.g. BS 2915 (14). Pressure relief devices shall be provided to prevent over-pressure of the outer jacket. The devices shall be suitable for the prevailing environmental conditions. 7

14 1.4.4 Under-pressure Prevention Devices Pits Where necessary, the inner vessel shall be equipped with under-pressure (vacuum) prevention devices to prevent collapse of the vessel by the development of partial vacuum conditions in the vessel. Partial vacuum conditions can arise due to excessive liquid withdrawal rates, by introducing super-cooled product into a partially filled inner vessel or, under certain conditions, sudden increases in atmospheric pressure. To avoid partial vacuum conditions, correct operating procedures shall be introduced and periodic checks made to ensure the under-pressure prevention device is in working order. Frequent demands on the vacuum relief valve may give rise to ingress of excessive quantities of moist air resulting in accumulation of ice and subsequent blockage of the relief valve piping. Pressure raising coils should be appropriately sized to prevent regular operation of vacuum relief valves. Equipment requiring regular attention or maintenance should not be installed in pits. Where the installation of equipment in pits is unavoidable, the inclusion of flanged joints and other potential sources of leakage should be minimised as a means of preventing the formation of a local oxygen deficient atmosphere. In these circumstances notices shall be positioned adjacent to the pit warning personnel of a potential asphyxiation hazard and that entry to the pit is forbidden unless specific precautions are observed, including as a minimum, analysis of the pit atmosphere and the issue of an entry permit. For further information on oxygen deficiency and entry into confined spaces see IGC Document 44/90/E (15). As a minimum, procedures shall comply with the requirements of the Confined Spaces Regulations 1997 (4) Electrical Equipment Electrical equipment necessary for the installation shall be to BS EN protection class IP54 or better (16). For more severe environmental conditions IP55 (designed to protect against water jets) or IP65 (designed to eliminate dust and protect against water jets) should be used. Consideration should be given to earth bonding of the installation pipework. All electrical installation shall comply with current electrical legislation Couplings Couplings used for the transfer of liquid argon and nitrogen shall be noninterchangeable with those used for other products. 8

15 1.4.8 Lighting Lighting of adequate intensity shall be provided for all working areas so that operations can be carried out safely at all times. The need for emergency lighting shall be considered Pipework The pipework shall be marked to identify the product transported. Valves shall be marked for function where appropriate Control and Instrumentation The installation shall have the following features: a) Two independent means of indicating high liquid level b) Automatic pressure make-up c) Automatic pressure vent and vacuum relief (the latter does not apply to vacuum insulated tanks) d) Pressure indication e) High and low pressure alarms f) High liquid level alarm Outer Jacket Purge Non-vacuum insulated jackets shall be provided with a dry-nitrogen purge system to maintain a positive pressure at all times to prevent the ingress of atmospheric air and ensure that the insulation is kept dry and ice free. This is particularly important with liquid nitrogen storage tanks as liquid air can condense causing oxygen enrichment and metal embrittlement of the outer jacket and support structure. 2. LAYOUT OF THE INSTALLATION 2.1 General The best guarantee for safe operation and prevention of dangerous leakage is the strict adherence to nationally accepted design and construction codes for storage installations and to specific routine operating instructions. The installation shall be sited to minimise risk to personnel, local population and property. Consideration shall be given to the location of any potentially hazardous processes in the vicinity, which could jeopardise the integrity of the storage installation. An installation may, because of its size or strategic location, come within the scope of specific planning control. If so, the siting of any such proposed installation shall be discussed and agreed with the local authority. 9

16 2.2 Safety Distances Basis The safety distances given in Appendix 3 are based on experience and calculations of minor releases and are not intended to protect against catastrophic failure of the liquid storage vessel. This philosophy is supported by previous operating history Definitions and Intentions The distance from the exposure to all of the following points on the storage installation must be equal to or be greater than the appropriate safety distance: a) Any point on the storage system where in normal operation leakage or spillages can occur (e.g. hose couplings, relief valve vents, etc) b) The tank outer jacket c) The tank nozzles or fill connections. Safety distances are intended to d) Protect personnel from exposure to an oxygen deficient atmosphere or cryogenic burns (see Appendix 2) in the event of a release of liquid. e) Protect the installation from the effect of thermal radiation or jet flame impingement from fire hazards. These distances are based on the storage pressure, ground roughness, likely weather conditions and an assumed vapour cloud release rate from the maximum diameter of liquid phase pipework on the storage installation and take into account site topography and provision for containment or diversion of the liquid spillage. These safety distances have been derived from those contained in BCGA CP20 (2), which are based on calculations provided by the Health & Safety Executive using SRD programme CRUNCH On-Site Risks The safety distances given in Appendix 3 are intended to protect storage installations, together with personnel and the environment within the site boundary, in conjunction with the following precautions: Taking into account topography, containment or diversion of spillage Careful siting of storage to allow for likely movement of vapour clouds Provision of emergency isolation valves Implementation of emergency procedures Adequate personnel training. 10

17 These distances are the minimum required to give adequate protection against risks involved in the normal operation of liquid argon and nitrogen storage installations and shall be observed. It is recognised that it is not reasonably practicable to define safety distances, which alone give adequate protection in the event of a continuous release of liquid from storage installations. The distances indicated in Appendix 3 correspond to well-established practice resulting from 485,000 tank years of service (2000). Should any evidence become available which indicates that a revision of the safety distances, in this document, is necessary then such a revision will take place Off-Site Risks To enable the site operator to minimise the risk to the general public and the environment it is necessary for each of the likely risks and exposures to be considered individually. The assessment of the risks should take into account the package of precautions provided within the site boundary but shall recognise that on-site emergency procedures and personnel training cannot normally be applied outside the site. 2.3 Location of Installation Outdoor Installation Liquid argon and nitrogen storage installations at production sites shall be situated in the open air in a well-ventilated position. The installations shall not be located inside buildings Protection Against Electrical Hazards The location shall be chosen so that damage to the installation by electric arcing from overhead or other cables cannot occur. The storage tank(s) shall be protected against lightning discharge. Reference to BS 6651 should be made for guidance on lightning protection (17) Level and Slope The slope of the ground shall be such as to provide normal surface water drainage, and shall take into consideration the prevention of directing hazardous materials, such as oil, towards the installation, and to the prevention of directing liquid spillage towards vulnerable materials or locations where people are at risk. Where liquid storage tanks are required to be installed at an elevated level, they shall be supported by purpose-designed structures. Consideration should be given to protecting these structures from cryogenic spillage. 11

18 2.3.4 Position of Vents All argon or nitrogen vents including those from relief devices shall be directed so as to avoid the risk of impingement on personnel, buildings, or structural steelwork. For the separation distance from flammable gas vents see Appendix Vapour Clouds All cryogenic liquid spillages or venting operations produce vapour clouds which are visible. Tests and calculations show that the extremities of the visible cloud are non-hazardous. When siting the installation, due consideration shall be given to the possibility of the movement of vapour clouds (resulting in decreased visibility or oxygen deficiency). Local wind conditions and the topography shall be taken into account. Vapour clouds from releases are generally low lying (typically below waist height). Such vapour clouds may be quite extensive depending on weather conditions and persons working below ground or at low level in the vicinity may be at risk. Guidance on emergency procedures is given in Diversion of Spillage The maximum liquid spillage, which may occur due to failures of associated equipment, other than the main storage tank itself shall be determined, and provision made to contain or divert it towards the safest available area. Arrangements should be made to run fire hoses to the storage area in the event of an emergency. These hoses may be used to produce a water spray for diverting a vapour cloud or liquid spillage from vulnerable areas Protection of Other Areas The site layout shall provide protection from liquid spillage for vulnerable areas, such as places where people may congregate, steel structures and other foundations. This protection may be achieved by the slope of the ground, provision of kerbs, gulleys or barriers of adequate size. Drainage systems within the distance specified in Appendix 3 shall be provided with traps to prevent the ingress of liquid or gaseous argon or nitrogen. Untrapped drainage systems shall be at least the distance specified in Appendix 3 from the installation. 2.4 Liquid Transfer Area Location of Area A road tanker, when in position for filling from or discharging to the installation, shall be in the open air and not in a walled enclosure from which the escape of 12

19 liquid or heavy vapour is restricted. Tankers should have easy access to and from the installation at all times. Kerbs or barriers shall be provided to prevent damage to any part of the installation by the tanker or other vehicles Construction of Access Apron The access apron is defined on page 1 of this Code of Practice and should be constructed and laid out in accordance with Appendix 4. Provision shall be made for diverting any liquid spillage. The materials used shall be suitable for use with cryogenic liquids and cold vapours, e.g. concrete or other non-porous materials. The tanker hard standing is not normally regarded as part of the access apron Control of Tanker Operation Operating personnel shall have unobstructed freedom of movement between the tanker and valve controls on the installation at all times. All tankers shall be provided with a positive means of preventing tow-away accidents. Such devices shall be fail-safe in operation and regular checks on the operation of such devices shall be included in maintenance procedures. Operating procedures shall be written to take account of such means. Reference should be made to Carriage of Dangerous Goods by Road Regulations 1996 (18). The vessel shall be adequately protected against over-pressure from the road tanker Reference EIGA publication 59/98 (29). 2.5 Liquid Transfer Pumps Ground mounted pumps for the transfer of liquid argon or nitrogen should be located in a well-ventilated area, away from personnel thoroughfares where practicable. 2.6 Isolation Valves Emergency Isolation Valves All bulk storage tanks of 200 tonnes capacity and above, fitted with liquid withdrawal or pump suction lines of 50mm bore or greater, shall be provided with an emergency isolation valve. It may be located internally or outside the tank. Internal location should be applied wherever possible. If externally located, it should be as close as possible to the tank to prevent the bulk flow of liquid from the vessel in the event of a line failure downstream of the valve. The emergency isolation valve is additional to the normal isolating valve required for process operation. The emergency isolation valve shall be reliable and quick acting and shall be capable of operation under conditions of heavy liquid spillage. The valve shall fail safe in a closed position on failure of operating power or operating fluid supply. Provision shall be made for operation from relatively safe point(s) remote from the potential area of flow of leaking liquid. The locations of the operating points, their purpose and mode of operation shall be clearly indicated by suitable notices. 13

20 2.6.2 Secondary Isolation Valves All bulk storage vessels for liquid argon and nitrogen shall be provided with at least two independent means of isolating the liquid withdrawal or pump suction pipelines. This can include emergency isolation valves, provided they are designed for tight shut off, and process isolation valves as specified below Process Isolation Valves 2.7 Foundations Any primary process isolation valve shall be located as close as practical to the vessel itself, but downstream of any emergency isolation valves. The position of isolation valves shall be such that they are subject to an acceptably low risk from damage from external sources. Protection against overpressure must be installed between any two isolation valves, where liquid or cold vapour can be trapped. The tank foundations shall be designed to withstand safely the weight of the tank, its contents and other possible loads resulting from wind, snow, water content during pressure test, etc. Subsidence conditions should be considered where appropriate. Where necessary, heating shall be provided to prevent ground freezing and consequent frost heave. 3. ACCESS TO THE INSTALLATION 3.1 Personnel The installation shall be so designed that authorised persons shall have easy access to and exit from the operating area of the installation at all times. 3.2 Access to Installation Controls Filling connections and equipment controls shall be located in such a way that easy access is provided. Filling connections and associated equipment controls should be located close to each other. The tank and tanker controls shall be visible and easily accessible from the operator s position. 14

21 3.3 Notices General Precautions Notices shall be clearly displayed to be visible at all times on or near the tank, particularly at access points. The following should be considered: LIQUID ARGON or LIQUID NITROGEN AUTHORISED PERSONS ONLY ASPHYXIANT HAZARD Wherever possible, symbols should be used and supported by written notices as necessary, e.g.: These signs shall comply with the Health and Safety (Safety Signs and Signals) Regulations 1996 (19) and with BS 5378 Safety Signs and Colours Parts 1, 2 and 3 (20) Identification of Contents The storage tank should be clearly labelled LIQUID ARGON or LIQUID NITROGEN. The connection fittings of multi-storage installations or long fill lines shall be clearly marked with the contents or the chemical symbol in order to avoid confusion. (See also 1.4.7) Legibility of Notices All displayed warning signs and labels shall be legible, visible and up-to-date at all times Operating and Emergency Instructions Operating and emergency instructions shall be available and understood before commissioning the installation. (See also 6.4). These instructions shall be kept up-to-date. 15

22 4. TESTING AND COMMISSIONING 4.1 Testing of Installation Prior to testing and commissioning, measures shall be taken to ensure that the systems have been designed and constructed in accordance with recognised pressure vessel/piping system codes and that all statutory requirements have been met. (See also 1.4.1). These measures will normally take the form of a review of drawings of pressure vessels and piping systems, manufacturing certificates and construction specifications. Checks shall also be made to ensure that the cleanliness requirements of paragraph have been met. In addition, the following tests shall be carried out in accordance with approved procedures Pressure Test Works manufactured storage tanks and pressure vessels of the installation will normally already have been tested/inspected in compliance with the relevant Pressure Vessel Code in the manufacturer s workshop prior to the first installation. Further pressure tests shall not be carried out on the vessel without reference to the vessel design documents and tank history. Site erected vessels/systems shall be subjected to a pressure test in accordance with the design codes and appropriate standards in order to ensure the integrity of the installation. Precautions shall be taken to prevent excessive pressure in the system during the test. Following any hydraulic test, the system/equipment shall be drained, thoroughly dried out and checked for moisture content. Care should be taken to prevent a vacuum condition arising in the inner vessel during draining. Where a pneumatic test is specified, the appropriate safety precautions shall be taken and nitrogen or dry, oil-free air shall be used as the test medium. The pressure in the system shall be increased gradually up to the test pressure. Pneumatic pressure testing is potentially hazardous and should be carried out in accordance with HSE Guidance Note Safety in Pressure Testing GS4 (21). Any defects found during the testing shall be rectified in an approved manner and the system then retested. A leak and function test shall be carried out in accordance with GS4 and at a pressure in accordance with the applicable code or regulation. Pressure tests / leak tests shall be witnessed by a Competent Person and a test certificate signed and retained in the tank dossier. 16

23 4.1.2 Pressure Relief Devices Relief valves shall have been subjected to a successful functional test and certified as such. (See Appendix 5). A check shall be made to ensure that any gagging pins, transit-locking devices/plugs have been removed from pressure relief devices of the inner vessel; outer jacket and piping systems and that the devices are undamaged, and lead seals are intact. The relief device set pressure (stamped on or attached to each device) shall be checked to see that it is in accordance with the maximum permissible operating pressure of the system Under-pressure Prevention Devices A check shall be made to ensure that any transit locking devices have been removed and that the under-pressure prevention device is undamaged Supports A check shall be made to ensure all relief valve or bursting disc vent lines are positioned such that they cannot impact on personnel or equipment and that the valves and vents are properly supported to take into account reaction forces. 4.2 Adjustment of Process Control Devices Process controls shall be adjusted to the required operating conditions of the system and then be subjected to a functional test. 4.3 Posting of Notices Notices (as defined in 3.3) shall be posted before putting the installation into service. 4.4 Commissioning Commissioning shall only be carried out by authorised personnel and in accordance with a written procedure. 5. OPERATION, INSPECTION AND MAINTENANCE 5.1 Operation of the Installation Only authorised persons shall be allowed to operate the installation. Written operating instructions shall be supplied to operating personnel and shall reflect current practices. The instructions shall define the safe operating limits of the system and any special procedures, which may be required to operate the system in an emergency situation. In general such instructions should be written and presented in a clear concise format. 17

24 If, during the operation of the installation, an excursion occurs outside the design or safe operating limits of the system (e.g. over-pressure, rapid temperature change, mechanical damage, etc), it shall be recorded in the tank dossier and a programme of inspection shall be drawn up by a Competent Person and implemented. 5.2 Periodic Inspection and Maintenance General The introduction of the Pressure Systems Safety Regulations (2000) (22), which will be referred to as the Regulations in this Code of Practice, has introduced specific requirements covering design, manufacture, installation, operation, maintenance and examination of pressure systems. BCGA Code of Practice CP24 (23) details the requirements of the preceding similar Regulations as applied to cryogenic liquid storage systems at production sites. For the purpose of clarification in this document, the terms inspection, checks and regular test are activities associated with the normal operation of the installation. The term Examination means examination in accordance with the Written Scheme as detailed in the Regulations and CP24. The site should be inspected regularly to ensure that it is maintained in a proper condition and that safety distances are respected. A comprehensive installation dossier shall be held on site. This dossier shall include: Process and instrumentation diagram(s) Tank dossier Operating instructions Written Scheme of Examination Maintenance programme Tank Installation An annual external visual inspection should be carried out by a Competent Person in accordance with a Written Scheme of Examination to confirm the satisfactory condition of the outer containment jacket and associated exposed pipework, valves, controls and auxiliary equipment. Periodic examination of the tank support structure should be carried out where appropriate. When a tank is taken out of service for modification or maintenance the accessible areas of the tank including the outer jacket, inner vessel, pipework, valves, controls and auxiliary equipment should be examined by a Competent Person, prior to recommissioning. 18

25 Periodic monitoring should be carried out of either the insulation space vacuum or, for non-vacuum tanks in argon service, the composition of the purge gas in the insulation space. This will identify the existence of any inner vessel leaks and confirm that the purge is still effective. A leak on an inner vessel may also be identified by rising insulation space pressure or cold patches on the outer jacket. The supply of purge gas to large non-vacuum insulated tanks should be checked periodically to ensure an effective purge is being maintained (this is particularly important with liquid nitrogen storage tanks). When soil conditions are uncertain, a regular monitoring of the stability of the tank foundations should be carried out Inner Vessel After manufacture and prior to commissioning, the inner vessel shall be validated as fit for service for a defined period by a Competent Person. (See 1.4). Thereafter the vessel should be revalidated periodically while in service. Revalidation should be based on a documentation assessment and an assessment of the vessel condition. The documentation assessment should include consideration of the original design code and amendments which may have occurred in the intervening period, the history of the vessel in service, experience with similar vessels elsewhere and any change in operating conditions. The assessment of the vessel condition should be based on a written scheme agreed by the operator and a Competent Person. This will be influenced by the documentation assessment, the established periods between revalidation, foreseeable modes of failure, particular features of the vessel design and contents, the possible detrimental effects of re-warming the inner vessel and, contamination. There are sound technical and operational reasons for not warming up a vessel to ambient temperature. The specific revalidation requirements for the vessel and the required frequency shall be defined and confirmed in writing by the Competent Person, for inclusion in the tank dossier, taking into account the documentation assessment and the assessment of the vessel condition. This shall equally apply to vessels already in service prior to the issue of this Code of Practice. Guidance on assessment is given in BCGA Code of Practice CP25 (24) Pressure Relief Devices Requirements for relief device inspection and testing are given in Appendix 5, which is derived from IGC Document 24/83 (25). 19

26 Regular visual inspection of the devices shall be carried out during normal operation. Bursting disc elements may deteriorate due to aggressive environments resulting in their relief pressure rating being reduced. It may therefore be necessary to replace disc elements, in such environments, on a planned basis Emergency Isolation Valve(s) Emergency isolation valves should be periodically tested in accordance with a prescribed procedure to check correct functional operation Ancillary Equipment Ancillary equipment (other than previously detailed) shall be maintained so as to be safe. 5.3 Opportunity Examinations When a tank is to be taken out of service, consideration should be given to making a detailed examination of the inner vessel to assess its condition and, in addition, provide data for revalidation of similar tanks. 6. TRAINING AND PROTECTION OF PERSONNEL 6.1 Training of Personnel All personnel directly involved in the commissioning, operation and maintenance of liquid argon or nitrogen storage systems shall be fully informed regarding the hazards of oxygen deficient atmospheres and cryogenic liquid and vapour burns. They shall be properly trained to operate or maintain the equipment. Training shall be arranged to cover those aspects and potential hazards that the particular operator is likely to encounter. Training shall cover, but not necessarily be confined to, the following subjects: Potential hazards of argon or nitrogen Site safety regulations Emergency procedures Use of fire fighting equipment Use of protective clothing/apparatus including breathing sets where applicable First aid treatment for cryogenic burns. In addition, individuals shall receive specific training in the activities for which they are employed. 20

27 It is recommended that the training be carried out under a formalised system and that records be kept of the training given and, where possible, some indication of the results obtained, in order to show where further training is required. The training programme should make provision for refresher courses on a periodic basis and for changes of site personnel. 6.2 Permit to Work Before maintenance is carried out on the installation, a written Permit to Work for the particular type of work (cold work, hot work, entry of vessel, electrical work, etc), shall be issued by an authorised person to the individual(s) carrying out the work. 6.3 Entry into Vessels Before entering any tank, vessel or inter-space during maintenance or decommissioning, it is essential that the equipment is safe for the work to be carried out. The following precautions, which are not necessarily all those required, shall be observed and included as conditions for the issue of the Permit to Work: Complete emptying and purging of the vessel contents Confirmation that the inner vessel is approximately at ambient temperature before entry is permitted Analysis of the atmosphere in the vessel and the inter-space at several selected points with a suitable gas detector (probes may be necessary) to ensure that the oxygen content is in the range 20 to 21%. It may be necessary to measure this regularly or continuously and to install forced ventilation while work is in progress Complete isolation of the inter-space purge lines and of process lines from other equipment, which may still be in service, by physical disconnection of a section of pipeline. Blanking discs may be used but they must be of appropriate material and thickness for the gas pressure in the pipe Presence of standby person(s) outside the tank adjacent to the access manhole to monitor the work in progress and provide assistance in the event of an emergency Use of appropriate safety equipment (harnesses, protective clothing, fire extinguishers, etc) Availability of rescue equipment (harnesses, self contained breathing apparatus, winches, radio links, etc) The Confined Spaces Regulations (4) shall be consulted for more detailed information on this subject. 21

28 6.4 Emergency Procedures Emergency procedures shall be prepared by the site operator to include action to be taken in the event of spillage of liquid argon or nitrogen. For general guidance on preparing an emergency plan see HSE booklet HS(G)191 (26). Local emergency services shall be party to the preparation of the emergency procedures. Works employees likely to be affected shall know the actions required to minimise the adverse effects of a spillage. Consideration should be given to practising emergency procedures. The following are guidelines, which should be used for formulating emergency procedures: Raise the alarm Summon help and emergency services Isolate the source of argon or nitrogen if appropriate and where safely possible Immediately evacuate all persons, particularly those working below ground level, from the danger area and seal it off Alert the public to possible dangers from vapour clouds in the immediate vicinity and evacuate when necessary. After the liquid spillage has been isolated, carry out oxygen deficiency checks on any enclosed areas where the vapour cloud may have entered. This includes basements, pits and confined spaces. 22